This invention relates to data backup, and is concerned particularly although not exclusively with the backup of data from a computer onto a tape.
Personal computers (PCs) are increasingly used in a wide range of applications. Such is the widespread use of personal computers that many homes are now equipped with a personal computer for word processing, managing personal finances, playing games, education and work related topics. This has inevitably required computers to hold large amounts of information and programs. Early machines had limited hard disk capacity, typically 50 megabytes or less. However, hard disk capacities of 500 megabytes are commonplace for newer machines. This poses a problem for the owner of either the old or new type of machine. The problem with the old machine is how to store more data, and for the new machine how to ensure that data is not lost. The hard disk is one of only a few mechanical components within a modern computer, and as such it is susceptible to wear which can cause data errors. An additional problem is that of software viruses that attack data structures with the outcome being data loss.
One solution to both problems is to use a tape backup unit. This would allow important files to be duplicated so as to ensure that a copy can be held in a safe place. Also, less frequently used files could be archived onto tape, which would free valuable disk space for additional files. Such tape backup disks exist, but are too expensive for many home users. A more economical method of data backup is required.
Most homes are equipped with video recorder equipment. Video recorders have been available for some time and are available in many different forms with varied signal characteristics. These machines were designed to record picture information which by its nature can accommodate many errors that would not be perceptible to a viewer. A video recorder can be used to store information other than pictures. However the information must first be converted into a form that the recorder accepts, a video signal.
It is possible to produce an interface for connecting a video recorder to a PC. Such a system would allow the user to back up information, thereby guarding against loss and allowing space to be freed up for storage of new information. Systems of this type have been proposed. However, they tend to be expensive and suffer from poor performance, due to varying capabilities of video recorders and tape media, and varying degrees of wear in video mechanisms.
The widespread use of inexpensive video backup systems has been limited by the varied specification of PCs relating to disk capacity, disk I/O bandwidth, system memory and processor speed, compounded by the varying capability of a domestic video recorder in terms of bandwidth and errors.
Preferred embodiments of the present invention aim to provide improved systems that can overcome the vagaries of differing PC specifications and video recorder capabilities. Another aim of preferred embodiments of this invention is to provide a programmable system that can be switched between several configurations.
Preferred embodiments of the invention aim to calculate the best possible conditions for each machine/tape combination and automatically modify a data rate, error correction and/or coding scheme accordingly. A further aim is to be able to compensate for differing PC specifications, by arranging data into frames whereby missing data can be identified and replaced with dummy data which is subsequently passed to an error correction process. A further aim is to divide the task of data encoding/decoding and error correction between a PC microprocessor and the data processing capabilities of an interface card, in order to achieve the lowest cost implementation of the back up system. A further aim is to provide the user with information allowing rapid identification and recovery of selected files.
More generally, according to one aspect of the present invention, there is provided a data transfer system for transferring data between a computer and a video recorder/player, the system comprising:
generating means for generating a video signal;
coding means for coding data received from a computer;
mixing means for mixing such coded data with said video signal to carry said data on said video signal;
separating means for separating coded data from a video signal received from a video recorder/player;
decoding means for decoding data separated by said separating means; and
settable timing means for controlling the rate of transfer of data between a computer and a video recorder/player.
Preferably, at least part of said generating means, coding means, mixing means, separating means, decoding means and timing means are embodied as an interface device for cooperation with a computer.
Preferably, said interface device comprises a PC expansion card.
A system as above may include first ranging means for assessing data transfer rate and associated error characteristics of a video recorder/player, and providing a control signal or data to said timing means.
A system as above may include second ranging means for assessing data transfer rate and associated error characteristics of a computer, and providing a control signal or data to said timing means.
Preferably, said second ranging means is arranged to assess CPU performance, available static memory, disk capacity and disk I/O bandwidth of a computer.
Preferably, at least part of said first and/or second ranging means is embodied by way of a program within said computer.
Preferably, for the data carried on said video signal, a predetermined number of data bits are carried on each of a plurality of lines of the video signal; each line carries markers to define the beginning and end of the line; and when decoding the video signal, missing data bits on a line are replaced by a predetermined sequence of bits, and each said sequence of bits is detected by an error detector and reconstituted by the original bits by an error correction process.
Preferably, said predetermined sequence of bits comprises a string of zero""s or a string of one""s.
Preferably, said decoding means comprises a counter which is reset by each transition edge of incoming data and provides a count signal after one-half of the duration of one data bit and thereafter at a period equal to the duration of one bit until being reset, the count signal being used to detect a current data bit.
A system as above may include means for generating a display signal to display identification data of a current file of which the data is being transferred between a computer and a video recorder/player.
In use, the data of such a display signal is preferably visible when playing back a tape via a TV or monitor connected to the video recorder/player.
The invention extends to a combination of a computer and/or a video recorder/player together with a data transfer system according to any of the preceding aspects of the invention.
Preferably, the data transfer system is arranged to back up data from a hard disk of the computer to the video recorder/player, and to restore data from the video recorder/player to the hard disk of the computer.
For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: